Through the efforts of the Human Genome Project and other large-scale investigations, it has become clear that the molecular origins of human complexity, disease, and distinctness from other organisms are rooted in more than just the number of genes in the genome. RNA editing, the post-transcriptional alteration of genome-encoded information by chemical modification of individual RNA bases, provides a potentially powerful way to diversify the set of RNAs expressed in an organism's tissues over time. Aberrant RNA editing has been implicated in human neurological diseases such as amyotrophic lateral sclerosis, epilepsy, depression, suicide, glioma, and cancers, and may have contributed to the evolutionary development of human neurobiology and cognition. While numerous RNA editing sites have been identified to date, we are still far from possessing a complete list of RNA editing targets particularly in the coding regions, thus hindering a full understanding of the complexity of this process and its potential for therapeutic intervention. We propose to extend our recent success at developing experimental and computational frameworks to the generation of a comprehensive atlas of RNA editing sites in humans and mice. By combining multiple validated techniques, we will rigorously quantitate RNA editing in a spectrum of matched human and mouse tissues from multiple developmental stages. We will use this approach to extend our analysis to RNA editing in other primates such as chimpanzees and rhesus macaque monkeys, with the expectation of uncovering the contributions of RNA editing to conserved functions as well as to human-specific neural evolution. We will also carry out large-scale computational analysis to search for RNA editing-related functional elements in the annotated genomic and transcriptomic datasets. Finally, we propose to use a variety of mouse strains mutated for the enzymes that perform RNA editing to elucidate the regulation of RNA editing. Taken together, the goals of this proposed project will deepen our understanding of the molecular basis of RNA editing, generate a set of experimental and computational tools to drive innovation in the RNA editing field, and unravel the network of signals that regulate RNA editing spatiotemporally, thus bringing us closer to the goal of manipulating RNA editing to alleviate human disease.